Stabilized fabric seam for flat-woven continuous fabric belts

ABSTRACT

A continuous fabric belt with intersecting threads and a method to produce the belt, so that within fabric seam region at least two strip-shaped regions which extend over the entire width of fabric seam and contain meeting points are arranged between strip-shaped fabric regions in which there are crossovers between warp- or machine directional threads and weft or cross-machine directional threads. The crossovers are materially connected by transmission welding.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP2012/052892, entitled “STABILISED FABRIC SEAM FOR FLAT-WOVEN CONTINUOUS FABRIC BANDS”, filed Feb. 21, 2012, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The current invention relates to continuous fabric belts for use in machines for the production of paper and relates in particular to the formation of fabric seams to connect the ends of the fabric belts in order to produce continuous fabric belts.

2. Description of the Related Art

Papers of various types, cartons and cardboards are summarized under the generic term of paper. Production of paper generally begins with the formation of a fibrous web from a fiber stock suspension in the forming section of a paper machine. The suspension and the fibrous web created therefrom through dewatering is supported on a continuous belt which—redirected through rollers—revolves within the forming section. Sheet formation is continued in downstream sections of the paper machine by further dewatering of the fibrous web, whereby the fibrous web is transported also in these sections by being supported on clothing in the embodiment of a continuous belt.

For rapid dewatering of fiber stock suspension and fibrous web the transport belts used in the individual sections of the paper machine, for example in the forming-, press- or dryer section are equipped with passages through which moisture in the form of water, steam and in the case of through-air dryers in particular also moist air can migrate from one side of the belt to the other side. In some sections, for example in the press sections the passages additionally serve to temporarily store moisture.

In flat woven fabrics the water permeability is secured through the hollow spaces which are formed by the intersecting yarns. Flat woven fabrics are such fabrics which do not have any nap, and which therefore do not have a two-dimensional structure. Flat woven fabrics can have smooth as well as structured surfaces. Yarn is to be understood to be a long, thin, flexible structure consisting of one or several fibers, that is one fiber or a fiber composite whose length exceeds its cross-sectional dimensions many times. In the production of fabric belts for use as paper machine clothing, polymer monofilaments are predominantly used, that is yarns produced from a polymer in the embodiment of a single fiber. Instead of monofilaments, twisted threads are often used in press felt base weaves which are composed of monofilaments or less often of staple fiber yarns. The fabric belts themselves can hereby form the clothing, or as is the case in the press section, can serve as a support substrate for further modified transport belts, for example press felts.

Various technologies are known for the production of continuous fabric belts, for example weaving on a circular loom or joining by weaving of pin seams for a detachable joining of the clothing ends. In the forming section and in through air dryers, flat woven fabrics produced from monofilaments are normally preferred which are joined by means of a so-called fabric seam to a continuous belt.

The production of flat woven continuous belts for clothing for use in paper machines begins generally by weaving a flat fabric belt in the form of a roll product, whereby the warp-, or respectively machine directional, threads progress in longitudinal direction of the belt, and the weft- or respectively cross-machine directional, threads progress transversely to the warp-, or respectively machine directional, threads between the lateral edges of the belts. With a view to improved mechanical strength as well as flexural rigidity the flat woven fabric belts are often structured to be two- or multi-layer, whereby the individual woven layers can differ from each other in regard to material, strength and direction of their yarns. By uniform meshing of yarns in one fabric layer into the weave of another fabric layer a stable flat bond can be established between the individual fabric layers.

The flat woven fabric belt in roll form is subsequently processed to length and the resulting partial pieces are joined through a seam connecting the leading edges to become continuous. The seam extends across the entire width of a continuous fabric belt and when designed as a fabric seam normally has a length of between 5 and 50 centimeters (cm) in the direction of travel of the belt. The direction of travel of the belt is hereby to be understood to be the direction of movement of the belt in intended use in a paper machine. For the respective segment of a continuous fabric belt carrying the fibrous web (or fibrous suspension) this direction is consistent with the transport direction of the fibrous web which is referred to as the machine direction.

So that the fabric seam does not cause marks on the fibrous web, the web's dewatering characteristics and surface structure must be as consistent as possible with the remaining continuous fabric belt which is referred to as full weave. Ideally the weave structure of the full weave continues in the fabric seam, for which however a weaving process that is to be carried out transversely to the weave direction of the full weave is required and which is carried out either manually or on weaving or sewing machines especially equipped for this purpose, for example on an accordingly customized jacquard weaving machine.

To produce the fabric seam the weft- or respectively the cross-machine directional threads are first released from the full weave at both face ends of a completed flat woven fabric belt in order to expose the ends of the warp threads or respectively the machine directional threads. The thus exposed warp- or respectively machine directional thread ends are subsequently interwoven with new weft- or respectively cross-machine directional threads to a complete woven formation, whereby the two ends of each warp- or machine directional thread are deposited in the same shed and each time are brought out of the fabric at a certain location and are later cut. In this weaving process the original warp threads thereby assume the role of the weft threads, and the weft threads assume the role of the warp threads, whereby the weft thread structure used for the fabric seam is normally obtained from a separate fabric belt strip by separation of the warp threads.

If both ends of a warp- or machine directional thread are brought out of the fabric and cut at the same location or respectively fabric pore, the ends of a warp- or machine directional thread more or less abut at this location. The strength of such fabric seams is based on the mechanical envelopment of the thread bends at the crossing points of warp- or machine directional threads and weft- or cross-machine directional threads. Due to the tensile stress on the continuous fabric belt during rotation in the paper machine the warp- or machine directional thread ends are pulled in opposite directions and can subsequently change their position relative to the weft- or cross-machine directional threads and possibly slip out from the thread formation. Especially the warp- or machine directional thread ends facing in the opposite direction to the machine direction are affected by this. Warp- or machine directional thread ends which have slipped out, protrude from the fabric and are preferably abraded during the rotation through the machine. This causes open areas in the fabric seam which reduce its tear strength and can lead to uneven drying and marking of the fibrous web.

To prevent the concentration of fabric stress to a small segment of the fabric seam and to increase its tear strength, the meeting points of the warp- or machine directional threads are arranged distributed over a region, normally approximately over the entire region of the fabric seam. The distribution of the meeting points can thereby assume a random or pseudo-random arrangement or an arrangement consistent with a scheme or pattern.

The breaking elongation of fabric seams as previously described however reaches only approximately one third of the breaking elongation of the full weave. In order to improve the seam strength, the length of the fabric seam—that is the extension of the seam in the direction of rotation of the continuous fabric belt—can be increased. However, the strength of the seam increases only sub-proportionally with the seam length, so that the improvement of strength on long fabric seams is not within an economic ratio to the production costs.

An improvement of the seam strength can also be achieved with the assistance of interlocks, whereby the ends of a warp- or machine directional thread can be brought out of the fabric at various locations so that the end regions of the warp- or machine directional thread are positioned adjacent to each other in the fabric over a certain distance. This overlapping of the warp- or machine directional thread ends however leads to a local reduction of the hollow spaces between the yarns with the result of a local impairment of the water and air permeability of the fabric and thereby to a different dewatering and drying characteristic compared to the full weave. An improvement in the seam strength through increasing of the interlock is moreover limited by the disproportionately lower increase in seam strength compared to interlock increase.

For strengthening of polymeric fabrics a material joining of warp- or machine directional and weft- or cross-machine directional threads by means of transmission laser welding is known. Welding of the yarns is normally carried at a laser wave length in the range of approximately 700 to 1200 nanometers (nm) which is not, or only very slightly absorbed by the yarns of the woven fabric. To be able to produce the heat necessary for welding of the yarns suitable light absorption zones have to be created. This may be accomplished by—possibly selective-coating of the yarns with special absorbers or dyes, or by use of yarn materials which already contain suitable absorption substances, for example soot, carbon nanotubes or dyes that absorb light waves in the aforementioned range. Transmission laser welding of yarn crossovers in the fabric seam region of a continuous flat fabric belt conducted in this manner results however in greater stiffness of the fabric seam, compared to that in a full weave.

What is needed in the art is a stabilized fabric seam per transmission laser welding of yarn crossovers for a continuous flat fabric belt and a method to produce same having lower stiffness as compared to that described above or respectively having a similar flexibility to the full weave of the continuous flat fabric belt.

SUMMARY OF THE INVENTION

The present invention provides continuous flat fabric belts with intersecting threads, at least the warp- or machine directional threads or the weft- or cross-machine directional threads are formed by yarns produced from a thermoplastic polymer which is transparent for light of a wavelength in a range of near infrared (NIR) and at least some of the yarns are materially joined with each other at crossing locations of warp- or machine directional threads and weft- or cross-machine directional threads by a material arranged at the yarn contact region of the crossing locations and absorbing light from the near infrared range. The thus materially joined crossover locations are hereby arranged within three or more than three strip-like, fabric regions in which no meeting point locations are disposed and which extend over the entire width of the flat fabric belt and which between them always define a fabric region containing meeting points. The term “transparent” in this document is to be understood that a medium which is transparent for light from a certain wavelength range does not absorb this light or absorbs it to only such a limited extent, for example a maximum of 10%, that no softening of the medium occurs.

A continuous fabric belt with accordingly produced stabilized fabric seam allows a deflection of energy affecting the meeting point of a warp- or machine directional thread by the materially joined thread crossovers before and after the meeting point to adjacent warp- or machine directional threads. This deflection of energy is improved through distribution of the meeting points to at least two fabric regions, since this ensures that each of the fabric regions containing meeting points is also traversed by warp- or machine directional threads which have no meeting points in this region. The distribution to several regions of the yarn crossovers formed for and materially joined for deflection of energy shortens the maximum width of a fabric region stiffened by the material connection and results thereby in a more flexible finish of the fabric seam region.

A meeting point may, for example, be a location where two ends of different warp- or machine directional threads or of one and the same warp- or machine directional thread are arranged along a straight line running toward each other.

If there are two ends running toward each other of different warp- or machine directional threads, then the warp- or machine directional threads running toward each other on the straight line can be such which are offset in the fabric by a maximum of five, for example a maximum of one weft- or cross-machine directional thread repeat, or by a maximum of two warp- or machine directional threads. As a result the warp- or machine directional threads of the seamed fabric then progress at an angle relative to the machine direction.

The ends can meet at the meeting point and not be woven together with a weft- or cross-machine directional thread, or can be interwoven together with one or several weft threads. In the first case the weave paths of the two warp-thread ends running toward each other meet. In the second case the weave paths of the two warp- or machine directional threads overlap. In both aforementioned examples the ends may make contact with each other.

It is also conceivable that the two ends running toward each other—viewed in machine direction—end at a distance from each other, whereby a maximum of two weft threads which are not interwoven with either of the two ends are arranged at the meeting point. In the latter case the weave paths of the two ends running toward each other end one, or a maximum of two weft- or cross machine directional threads removed from each other.

Viewed in the machine direction, the meeting point can extend from the last weft- or cross machine directional thread with which one of the two ends connects before it is brought out of the fabric to the last weft- or cross machine directional thread with which the other of the two ends connects, before it is brought out of the weave.

Embodiments of methods to create flat fabric belts having an appropriately stabilized fabric seam include steps for the creation of a flat fabric belt consisting of yarns of thermoplastic materials, whose warp- or machine directional threads and/or weft- or cross-machine directional threads are transparent for light of a wavelength in a near infrared range and at whose ends warp- or machine directional threads are exposed to form a fabric seam to join the ends of the flat fabric belt into a continuous fabric belt; to introduce a material absorbing the light from the near infrared wavelength into the yarn contact region of crossovers of the warp- or machine directional threads with weft- or cross-machine directional threads in the event that neither warp- or machine directional threads nor weft- or cross-machine directional threads absorb the light in the near infrared range, whereby the absorbing material is introduced into at least the yarn crossovers which are arranged within three or more than three strip-shaped fabric regions; wherein no meeting points are disposed and which extend over the entire width of the flat fabric belt and which between them always define a fabric region containing meeting points; and for radiation of the at least three or more than three strip-shaped fabric regions wherein no meeting points are disposed with light from the near infrared wavelength range for fusing the yarns at absorbing regions.

The near infrared range includes, for example, the wavelength range of between approximately 700 to 1200 nanometers (nm), so that conventional NIR transmission laser welding equipment and methods can be used for materially joining of the yarn transitions, for example by use of diode lasers having emission wavelengths in the range of 808 to 908 nm, of Neodymium-doped yttrium aluminum garnet-lasers (NdYAG-lasers) having an emission wavelength of 1064 nm or of infrared radiators.

To ensure an effective deflection of energy acting upon a meeting point, at least one of the fabric regions with materially joined crossover locations of warp- or machine directional threads and weft- or cross-machine directional threads is arranged within one fabric seam which joins the ends of a flat fabric belt into a continuous flat fabric belt.

When producing a greater number of fabric regions wherein meeting points are disposed compared to the length of the fabric seam, material regions containing one or two of the materially joined crossover points can reach at least partially into the full weave outside the fabric seam.

In embodiments having warp- or machine directional threads and weft- or cross machine directional threads which are transparent for the light in the near infrared range, material joining of the respective yarn crossover points is effected by absorption of light in a wavelength from the near infrared range through an appropriate light absorbing material arranged at the crossovers between warp- or machine directional threads and weft- or cross-machine directional threads, whereby selective fusing of the yarn crossovers which protects the polymer structure of the yarns can be achieved.

Alternative embodiments have warp- or machine directional threads which absorb light of a wavelength from the near infrared range and weft- or cross-machine directional threads which are transparent for light from this range, whereby material to material joining is effected at crossover points of both yarns by absorption of light of a wavelength from the near infrared range by the warp- or machine directional threads. Since in this arrangement only the yarn crossovers are materially joined where the light absorbing warp- or machine directional thread was radiated through the transparent weft- or cross-machine directional thread, only some of the yarn crossovers are materially joined in some of these embodiments. The result is that stiffening of the fabric is less than if all crossovers were to be materially joined, thus achieving greater flexibility of the fabric in the welding region, that is in the region of the materially joined yarn crossovers.

In an additional embodiment of the present invention the weft- or cross-machine directional threads, at least in the fabric seam region, are such that they absorb light from a wavelength in the near infrared range, whereby the warp- or machine directional threads are transparent for light from this range. Material to material joining of the yarns at the crossover points is hereby effected by the absorption of light having a wavelength in the near infrared range by the weft- or cross-machine directional threads. In this embodiment the use of welding light absorbing yarns is limited to the fabric seam region or possibly to a somewhat extended welding region so that the use of relatively expensive yarns can be reduced. Since in this case also only every second yarn crossover is materially secured, this embodiment offers a comparatively greater flexibility.

In order to materially join all yarn crossovers in a combination of absorbing threads and transparent threads crossing over them, the welding light is radiated into the fabric from both sides.

In embodiments of the method, the introduction of a material which absorbs light from the near infrared wavelength range into the yarn-contact region of crossovers of the warp- or machine directional threads with weft- or cross-machine directional threads of a material may include a step for the application of the absorbent material dissolved in a solvent, onto the at least fabric region or regions in which a material to material joining of yarn crossovers is provided, and for evaporation of the solvent.

In additional embodiments of the method the introduction of a material which absorbs the light from the near infrared wavelength range into the yarn-contact region of crossovers of the warp- or machine directional threads with weft- or cross-machine directional threads of a material may include a step for coating the warp- or machine directional threads of the flat fabric in the region of the ends with a light absorbing material prior to forming the fabric seam. A simple coating of the warp- or machine directional threads is hereby possible that is limited to the fabric seam region which, in combination with non-coated weft- or cross-machine directional threads provides the formation of more flexible welded fabric regions or which, in combination with coated weft- or cross-machine directional threads provides the formation of completely solid welding regions.

For selective fusing of the yarns at the yarn contact regions or points of the crossovers of warp- or machine directional yarns and weft- or cross-machine directional yarns the absorbent material is removed if required from outside the yarn contact points at the crossovers of warp- or machine directional yarns and weft- or cross-machine directional yarns by rinsing, washing or brushing.

To achieve increased tear resistance of the fabric seam when producing same, the meeting points in some embodiments of the present invention are arranged with materially joined yarn crossovers between two meeting point free fabric regions relative to the direction of the warp- or machine directional threads at several locations at a distance from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a flat fabric belt, prepared for joining the fabric seam according to the present invention;

FIG. 2 is a schematic illustration of a flat fabric belt such as the one illustrated in FIG. 1 closed with a fabric seam according to the present invention;

FIG. 3 a is a schematic illustration of a device for transmission welding of yarn crossovers in the region of the fabric seam of a continuous flat fabric belt such as the one illustrated in FIG. 2;

FIG. 3 b is a schematic illustration of another device for transmission welding of yarn crossovers in the region of the fabric seam of a continuous flat fabric belt;

FIG. 4 is a schematic illustration of material to material joints formed using welding light absorbing weft- or cross-machine directional yarns according to the present invention;

FIG. 5 is a schematic illustration utilizing welding light absorbing materials selectively arranged between yarn crossovers according to the present invention;

FIG. 6 is a schematic illustration of the basic principle of a fabric seam with low stiffness, stabilized by transmission welding; and

FIGS. 7 a-d illustrate various embodiments of meeting points of a belt according to the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown a schematic illustration of a flat fabric belt 10 produced to length with ends 3 and 4 prepared for the formation of a fabric seam. The warp- or machine directional threads 1 of fabric 10 extending in the horizontal direction, cross in a defined pattern with weft- or cross-machine directional threads 2 illustrated in the vertical direction. For the purpose of a clear illustration always only one warp- or machine directional, or weft- or cross-machine directional thread is given an identification number.

Moreover, for better illustration of features, distance and number of warp- or machine directional threads and weft threads, as well as weave and dimensions of flat fabric belt 10 are selected without reference to concrete characteristics.

To produce a continuous flat fabric belt, ends 3 and 4 of flat fabric belt 10 must be joined with each other. So that the joint does not display a different dewatering characteristic compared to the rest of the continuous flat fabric belt which could lead to markings on the fibrous web, ends 3 and 4 are connected with each other, thus creating a fabric seam. In preparation for this, the weft- or cross-machine directional threads were removed from the regions of the two ends 3 and 4, as illustrated in FIG. 1. Ends 3 and 4 therefore now only consist of warp- or machine directional threads. Since in region 5 which is located between the two ends 3 and 4 no threads, and in particular also no weft- or cross machine directional threads are removed, the original weave remains completely intact in this region 5 which is referred to as full weave.

As already previously mentioned, in order to create the fabric seam ends 3 and 4 of flat fabric belt 10 are joined together in a weaving process which occurs in the cross direction to the original weave direction of flat fabric belt 10. In this process, warp- or machine directional threads which were extricated from the weave at ends 3 and 4 are woven into a weft- or cross machine directional thread structure with the dimensions of the fabric seam. Even if in this seam weaving process the weft- or cross-machine directional threads 2 assume the role of the warp- or machine directional threads, and the warp- or machine directional threads lassume the role of the weft- or cross-machine directional threads the identifications referring to the original flat fabric belt 10 are maintained in this document in order to avoid confusion.

The length of the fabric seam, that is its extension in the direction of the travel continuous flat fabric belt 11 is smaller than the sum of the two fabric belt ends 3 and 4, so that the ends of each of the warp- or machine directional threads overlap each other in the fabric seam and would thereby reduce the permeability of the fabric seam for water, steam and air in contrast to the full weave. In order to avoid or reduce this effect the overlapping components of the warp- or machine directional threads are brought out of the fabric—generally on the same side of the fabric—through a fabric pore or through two adjacent fabric pores after which the protruding thread segments are cut off. Depending on how great the tension is which is exerted upon the protruding warp- or machine directional thread ends during cutting, the warp- or machine directional threads subsequently make contact within the fabric or are positioned at a slight distance from each other. At very low tension the ends of the warp or machine directional threads can also be bent to the surface of the fabric and if they are bent through the same fabric pore toward the outside, can touch one another in the region of the bend. If the ends of a warp- or machine directional thread are fed through different fabric pores this can also lead to an interlock, depending upon the location of the pores. The region in which the ends of a warp- or machine directional thread are located is referred to as meeting point.

The result of the fabric seam process is a continuous flat fabric belt 11 having a fabric seam 6 as shown in the heavily schematized illustration of FIG. 2. An illustration of the weave in the full weave region 5 has been foregone in this illustration in favor of emphasizing fabric seam 6. Moreover, in FIG. 2 the directional identifications used in this document are indicated. These are the direction of travel LR of continuous flat fabric belt 11 during intended use of a machine for the production of paper; the cross direction QR oriented transversely thereto of belt 11 and machine direction MR which represents the transport direction of a fibrous web on continuous flat fabric belt 11 in a paper machine.

Because of the discontinuance of the warp- or machine directional threads at the meeting points, no forces can be transmitted through the meeting points. All tensile load on continuous fabric belt 11 always results in an opening or respectively widening of the meeting points if the tensile forces acting upon the meeting points cannot be transferred to other threads in the fabric. In a fabric seam such a load transmission to other yarns at the crossovers of warp- or machine directional threads with weft- or cross-machine directional threads adjacent to the meeting point is possible. Since however the load transmission is limited due to static friction at the crossovers, the meeting points form a weak point in the fabric seam. The meeting points are normally distributed uniformly across the fabric seam in order to avoid a concentration of such weak points which would reduce the mechanical strength of fabric seam 6.

To improve the load transfer to adjacent yarns, yarn crossovers in fabric seam region 6 can be materially joined with each other. In order to stabilize uniformly distributed meeting points in a fabric seam through materially joining of adjacent yarn crossovers, appropriate joining of yarn crossovers must extend over the entire area of the fabric seam. At the materially joined yarn crossovers the threads can no longer move relative to each other, resulting in a stiffening of the fabric seam. Because of the stiffening, greater bending forces act upon fabric seam 6 during rotation of continuous fabric belt 11 in a paper machine then act upon the full weave 5, whereby belt 11 is heavily stressed, in particular at the transitions of the plate-like stiffened fabric seam 6 to the more flexible full weave 5.

To stabilize fabric seam 6 through materially joining of yarn crossovers and to keep it flexible in spite of this, the meeting points are arranged within certain sections of the fabric seam and the material to material joining of yarn crossovers is performed in different segments of the fabric seam or in the adjacent full weave.

Stabilization of the fabric seam connection through materially joining of yarn crossovers is accomplished with a previously discussed transmission welding process. For this purpose continuous flat fabric belt 11 is initially stretched, for example, by two rolls 25 and 26, as illustrated in FIGS. 3 a and 3 b, whereby at least one of the rolls is mounted movably for the purpose of stretching fabric seam 6, as illustrated in the drawing. The device may of course also include additional rolls with the assistance of which belt 11 can be redirected several times, thereby being able to provide a shorter configuration of the unit. Other suitable devices include a tensioning device, wherein only a section of the continuous flat fabric belt including fabric seam 6 is stretched, for example by clamp assemblies.

For welding of warp- or machine directional threads and weft- or cross-machine directional threads at the crossover points light 21 from laser 20 emitted in the near infrared range or radiated from an infrared radiator is directed onto the crossovers of warp- or machine directional threads and weft- or cross-machine directional threads which are to be welded. Suitable lasers are, for example, diode lasers having emission wavelengths in the range of 808 to 980 nm and Nd:YAG-lasers having an emission wavelength of 1064 nm. For example, lasers or infrared radiators with emissions in the range of approximately 700 to 1200 nm are used, since light in this wavelength range is not absorbed by the yarns of the fabric, or respectively not to an extent that would cause heating of the yarns.

In the device illustrated in FIG. 3 a, laser light 21 is emitted in a fan-shape from laser source 20 and is converged linearly by a roll 22 which is transparent for the radiated light onto the contact surface between roll 22 and fabric seam 6. The fan-shaped light beam can be produced by rapid diversion of the laser light or also statically by suitable optics. The laser energy concentrated linearly through roll 22 is converted into thermal energy by light absorbent substances arranged in the radiation region, which ultimately leads to fusing of the yarns in the region of the absorbing substances. The pressure exerted by roll 22 upon the fabric facilitates the material to material joining between the yarns making contact in a fusing zone.

In the device illustrated in FIG. 3 b fan-shaped welding light 21 (either laser light or light of a suitable infrared radiator) emitted from welding head 20′ is directed directly onto the fabric seam. The device therefore does not include a roll in the radiation process which is transparent for the welding light. In this device the contact pressure between the yarns at their crossover points brought about by thread guidance is used to facilitate a material to material joint. The contact pressure can be increased through tensioning of continuous flat fabric belt 11, for example with the assistance of the two rolls 25 and 26.

In the case of the devices illustrated in FIGS. 3 a and 3 b, moving laser head 20 (or another suitable light source) and roll 22 or laser head 20′ transversely to the direction of travel LR of continuous fabric belt 11 is sufficient for radiation of randomly selectable sections of the fabric seam, since moving of welding light 21 in the direction of travel of fabric seam 6 through rotation of rolls 25 and 26 can be performed. If however continuous flat fabric belt 11 is clamped to be immobile, then laser head 20 and roll 22 or respectively laser head 20′ can also be arranged to be movable in the direction of travel of the fabric seam.

For welding of yarn crossovers in the fabric seam region 6 the radiated light must be absorbed between the yarns contacting each other at the crossovers. For this purpose either one of the yarns crossing over each other can be formed such that it absorbs the light used for welding, or a suitable absorber is introduced between the yarns at the crossover points.

Yarns absorbing light in the near infrared range can be produced for example through introducing carbon, for example in the form of soot, graphite or carbon nanotubes into the thermoplastic base material. Absorber solutions for application onto the welding points are offered for example by the Clearweld Company. However, suitable colorants can also be used which are applied onto the yarns, dissolved in a solvent.

When using yarns which absorb welding light 21—so that some of the yarn crossovers can be welded—the yarns are used, for example, either as weft- or cross-machine directional yarns in the fabric seam region, or as warp- or machine directional yarns of the continuous flat fabric belt. The first case is illustrated in FIG. 4, wherein a sectional view through part of fabric seam 6 is illustrated in cross direction QR of belt 11. The illustration shows two weft- or cross-machine directional threads 2 arranged behind each other which cross over cross sectionally illustrated warp- or machine directional threads 1. Weft- or cross-machine directional threads 2 absorb welding light 21 which is radiated from above onto the fabric. The warp- or machine directional threads are transparent for this light. Welding light 21 therefore does not reach a yarn crossing which, in regard to the light radiation is covered by a weft- or cross-machine directional thread, so that these yarn crossovers are not fused by the welding light. At the other crossover points where the warp- or machine directional threads which are transparent for radiated welding light 21 are arranged above welding light 21 absorbing weft- or cross-machine directional threads, welding light 21 reaches the contact region between the yarns and can heat the weft- or cross-machine directional thread there, so that a material to material joint 7 of both yarns is caused at this location.

In order to be able to materially join all yarn crossovers in the welding region as illustrated in FIG. 5, the welding region is either radiated from both sides of the fabric with welding light, or solely yarns which are transparent for welding light 21 are used in the welding region. A welding light 21 absorbing material (not illustrated in the drawing) is introduced between the yarns at the crossover points of warp- or machine directional threads and weft- or cross-machine directional threads. Through an appropriately selective absorber application, welding light 21 can penetrate all yarns and is absorbed exclusively from the absorber material arranged between the crossovers which subsequently heats and leads to fusing of the surrounding yarn regions. Fusing of the yarn regions which contact each other ultimately leads to establish the material to material joint 7.

The selective introduction of absorber material into the crossover regions of the yarns can occur in different ways. In one embodiment, absorber solutions are used which contract during evaporation of the solvent component without leaving absorber residues on the surfaces that are no longer moistened.

Appropriate absorber solutions are marketed by the Clearweld Company. Due to the capillary effect associated with the moistening of the yarns the absorber solution retreats during evaporation of the solvent to the yarn crossover points where it enriches the absorbing material between the yarns.

With absorber solutions which, during evaporation of the solvent component leave the absorbing material behind on the yarn surfaces, for example inks, another embodiment of the selective absorber applications may be utilized, wherein the warp- or machine directional threads are coated with an absorber material in end regions 3 and 4 of fabric belt 10 prior to starting the fabric seam process, for example by immersion of the exposed warp- or machine directional threads in an appropriate absorber solution and subsequent drying of the threads. The weft- or cross-machine directional threads used to form the fabric seam may be, but do not have to be coated with an absorber material. In alternative embodiments, the fabric seam is soaked with an absorber solution, for example in an immersion bath or by spraying the solution on. The thus achieved coating thickness should be thin enough so that the pores do not become clogged. Examples are coating thicknesses to a maximum of approximately 60 micrometers (μm), or a maximum of 30 μm and further a maximum of 20 μm.

After completion of the absorber coated fabric seam, absorber material from outside the crossover regions is removed. This can occur through mechanical removal, for example brushing or wiping off with a cloth or similar device. The coated region of the fabric may however, be treated with a solvent for dissolving the absorber material, for example with a mixture of tetrahydrofuran (THF) (75%) and water (25%). In order to prevent the solvent from penetrating the crossover regions of the yarns, fabric belt 11 is put under tension in the treated region so that the contact pressure between the yarns is increased at the crossover points. For removal of the excess absorber material the fabric can be rinsed with the solvent. The removal may also be accomplished through wiping with a cloth soaked in solvent, or with the assistance of a brush.

After the selective absorber application the yarns are materially joined in selected regions of the fabric seam and possibly of the full weave at their crossover points. If instead of an absorber coating of yarn crossovers, welding light 21 absorbing yarns are used as described above, welding of crossover points is also only performed in selected regions of the fabric seam or of the full weave. If yarn crossovers are welded also in regions of the full weave, then absorption of welding light 21 at the respective crossover points is also ensured in these regions.

The selected regions contain no meeting points and are arranged on continuous fabric belt 11 so that each region of belt 11 containing meeting points is always arranged between two selected regions containing no meeting points. The basic principle of this arrangement is illustrated in FIG. 6. Continuous belt 11 illustrated schematically in the region of fabric seam 6 includes two regions 61 and 62 containing meeting points which are arranged between regions 71, 72 and 73 which contain no meeting points (indicated as dotted regions in FIG. 6) with welded yarn crossover points. For reasons of clarity the drawing only shows warp- or machine directional threads. The weft- or cross-machine directional threads which are obviously also contained in the fabric are however not depicted. Number, thickness and distance of the exemplified warp- or machine directional threads are omitted from the depiction of the basic principle and are not based on actual fabrics. Moreover, the distances of the warp- or machine directional threads at the meeting points are illustrated excessively large.

The meeting point of a warp- or machine directional thread 1 is located, for example, always in a region which is different from the region or regions in which the meeting points of the warp- or machine directional threads adjacent to the warp- or machine directional thread are located. This ensures that the tensile forces acting upon the warp- or machine directional thread in the region of its meeting point is diverted to and absorbed by the adjacent warp- or machine directional threads at the welding regions surrounding the meeting point. If using—as shown in FIG. 6—two meeting point containing regions 61 and 62, the meeting points of the warp- or machine directional threads are thus located alternatively in one or the other meeting points containing region, so that in each of the meeting point containing regions 61 and 62 tensile forces acting upon belt 11 are absorbed respectively by half of all warp or machine directional threads.

So that the meeting point containing regions can absorb greater tensile forces, more than two, for example three, four or more such regions must be arranged on the fabric seam, whereby here too the meeting points of adjacent warp- or machine directional threads are arranged in different meeting point containing regions, for example in such a way that in each of the meeting point containing regions, corresponding numbers of adjacently located warp- or machine directional threads have their meeting points arranged distributed across all of these regions. In three accordingly arranged meeting point containing regions the mechanical load is thus absorbed in each of these regions by two thirds of the warp- or machine directional threads, by four of three quarters of the warp- or machine directional threads and so forth. If, in a plurality of meeting point containing regions fabric seam 6 is too short to accommodate the outer meeting point free regions with welded yarn crossovers, then these can also be arranged completely or partially in full weave 5.

One specific embodiment of flexible fabric seam 6, arranged as described and at a length of the fabric seam of 300 mm includes two meeting point containing regions 61 and 62 which extend in cross direction QR of continuous belt 11 across the entire width of fabric seam 6 and which have a width of 60 mm in longitudinal direction LR of continuous belt 11. The meeting points are, for example, arranged within each of meeting point containing regions 61 and 62 according to a pattern offset relative to each other in direction of travel LR. Between meeting point containing regions 61 and 62 and adjacent to the outside of them, meeting point free regions 71, 72 and 73 are located with welded yarn crossovers which also extend over the entire width of fabric seam 6 and which have a width of 60 mm in longitudinal direction LR of continuous belt 11. In this form the length of the regions which are stiffened through welding is 60 mm in contrast to 300 mm of a fully welded fabric seam 6. Because of the small dimension of the welded regions in the direction of rotation of continuous flat belt 11, the belt is subjected to lower bending loads and is thereby more durable. By alternating welded regions and non-welded regions a sufficiently high number of yarn crossovers is provided for stabilization of the fabric seam without causing stiffening of the fabric, because between narrow stiffened zones there is always a highly flexible zone arranged.

Referring now to FIGS. 7 a-7 d, there are illustrated various options to configure meeting points T. FIG. 7 a illustrates meeting point T, wherein two ends 1 a and 1 b of one and the same warp- or machine directional thread 1 running toward each other can be seen. In the current example, ends 1 a and 1 b meet each other, whereby they connect over two immediately adjacent weft threads 2 a and 2 b and are directed together between these two weft threads 2 a, 2 b downward out of the fabric. Viewed in machine direction MD, meeting point T extends from weft thread 2 a to weft thread 2 b.

FIG. 7 b illustrates meeting point T, wherein two ends 1 a and 1 b of one and the same warp- or machine directional thread running 1 toward each other can be seen. In the current example, ends 1 a and 1 b meet each other, whereby they are interwoven with three immediately adjacent weft- or cross-machine directional threads 2 a, 2 b and 2 c, before ends 1 a, 1 b are directed out of the fabric. Viewed in machine direction MD, meeting point T extends from weft- or cross-machine directional thread 2 a to weft- or cross machine directional thread 2 c.

FIG. 7 c illustrates meeting point T, wherein two ends 1 a and 1 b of one and the same warp- or machine directional thread 1 running toward each other can be seen. In the current example two ends 1 a, 1 b—viewed in the machine direction—are directed out of the fabric at a distance of two weft- or cross-machine directional threads 2 a, 2 b from each other, whereby two weft- or cross-machine directional threads 2 a, 2 b which are not interwoven with either of the two ends 1 a, 1 b are arranged at meeting point T. Viewed in machine direction MD, meeting point T extends from weft- or cross-machine directional thread 2 a to weft- or cross machine directional thread 2 d.

FIG. 7 d illustrates meeting point T, wherein two ends 1 a and 1 b of one and the same warp- or machine directional thread 1 running toward each other can be seen. In the current example, ends 1 a and 1 b meet each other, whereby they are interwoven with one weft- or cross-machine directional thread 2 a, before ends 1 a, 1 b are directed out of the fabric. Viewed in machine direction MD, meeting point T is limited to weft- or cross-machine directional thread 2 a.

All embodiments illustrated in FIGS. 7 a-7 d are shown for ends of one and the same warp- or machine directional thread. Above described embodiments are however equally applicable for ends running toward each other of different warp- or machine directional threads.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

What is claimed is:
 1. A flat woven continuous fabric belt, comprising: a plurality of intersecting threads including a plurality of warp threads extending in a machine direction and a plurality of weft threads extending in a cross machine direction, at least one of said warp threads and said weft threads being formed from a plurality of thermoplastic polymer yarns which are transparent for a light of a wavelength in a range of near infrared, at least some of said yarns being materially joined with each other at a plurality of crossover locations of said warp threads and said weft threads with a material arranged at a yarn contact region of said crossover locations and which absorbs light from said near infrared range, said materially joined crossover locations being arranged within at least three strip-like fabric regions in which no meeting point locations are disposed, which extend over an entire width of the flat woven continuous fabric belt and which between said at least three strip-like fabric regions there is always defined a fabric region including a plurality of meeting points.
 2. The flat woven continuous fabric belt according to claim 1, wherein said near infrared range is in a wavelength range of between approximately 700 to 1200 nanometers.
 3. The flat woven continuous fabric belt according to claim 1, wherein at least one of said at least three fabric regions with said materially joined crossover locations of said warp threads and said weft threads is arranged within a fabric seam which joins a pair of opposing ends of a flat fabric belt into the flat woven continuous fabric belt.
 4. The flat woven continuous fabric belt according to claim 3, wherein said at least three fabric regions including one or two of said materially joined crossover locations reach at least partially into a full weave portion of the flat woven continuous fabric belt outside of said fabric seam.
 5. The flat woven continuous fabric belt according to claim 4, wherein said warp threads and said weft threads are transparent for said light in said near infrared range and wherein said crossover locations are materially joined by absorption of light in a wavelength from within said near infrared range through a light absorbing material arranged at said crossover locations between said warp threads and said weft threads.
 6. The flat woven continuous fabric belt according to claim 1, wherein said warp threads absorb said light from a wavelength in said near infrared range and said weft threads are transparent for said light from said near infrared range, and a material to material joining is effected at said crossover locations by absorption of said light in a wavelength from said near infrared range by said warp threads.
 7. The flat woven continuous fabric belt according to claim 1, wherein said weft threads absorb said light from a wavelength in said near infrared range and said warp threads are transparent for said light from said near infrared range, and a material to material joining is effected at said crossover locations by absorption of said light of said wavelength in said near infrared range by said weft threads.
 8. A method for creating a stabilized fabric seam, the method comprising the steps of: providing a flat fabric belt including yarn formed of a plurality of thermoplastic materials, said flat fabric belt including a plurality of warp threads extending in a machine direction and a plurality of weft threads extending in a cross-machine direction, at least one of said warp threads and said weft threads being transparent for a light of a wavelength in a near infrared range, said warp threads being exposed to form a fabric seam at a pair of opposing ends of said fabric belt; joining said opposing ends of said flat fabric belt into a continuous fabric belt to create a woven fabric seam; introducing a light absorbing material for absorbing said light from said near infrared wavelength into a yarn contact region of a plurality of crossovers of said warp threads with said weft threads if neither said warp threads nor said weft threads absorb said light in said near infrared range, said absorbing material being introduced into at least said crossovers arranged within at least three strip-shaped fabric regions where no meeting points are disposed and which extend over an entire width of said flat fabric belt, where between said at least three strip-shaped fabric regions there is always defined a fabric region containing said meeting points; and radiating said at least three strip-shaped fabric regions where none of said meeting points are disposed with said light from said near infrared wavelength range to fuse said yarns at a plurality of absorbing regions.
 9. The method according to claim 8, wherein said introducing step further comprises the step of coating said warp threads of said flat fabric belt in a region of said opposing ends with a light-absorbing material prior to said creation of said woven fabric seam.
 10. The method according to claim 8, wherein said introducing step further comprises the step of coating said plurality of yarns in a region of said woven fabric seam.
 11. The method according to claim 10, wherein said coating step further comprises the step of coating a plurality of yarns in an adjacent full weave region with said light-absorbing material.
 12. The method according to claim 11, further comprising the step of removing said absorbent material from outside said yarn contact regions at said crossovers of said warp threads and said weft threads by one of rinsing, washing and brushing.
 13. The method according to claim 12, wherein said step of joining said opposing ends of said flat fabric belt into a continuous fabric belt to form a woven fabric seam further comprises the step of arranging said meeting points relative to a direction of said warp threads at a plurality of locations at a distance from each other. 